Buying only food without packaging seems to exclude a lot of things to which our ancestors had access. Eggs and dairy, meat, noodles (unless you want to make your own flour from bulk wheat), any liquids...
http://original-unverpackt.de/
But I see this more as a political stance against the common package waste, not so much about about selling different food.
It's only a week.
As a matter of fact, I did start getting bulk wheat and grinding flour from it. When I started the experiment I had no expectation I'd end up making bread from scratch. Just one thing led to another and I started doing it. Now I can go from unground wheat berries to a hot loaf of bread in under an hour, so it's more convenient than buying, on top of being cheaper, healthier, and tastier. I haven't bought bread from a store since.
Getting a pressure cooker helped a lot too, which made cooking dry legumes quick and easy.